1. Field of the Invention
This invention relates to a disc cartridge having accommodated therein a disc on which predetermined information signals are recordable, or have been recorded, such as a magneto-optical disc or an optical disc.
2. Description of Related Art
There has previously been proposed a disc for recording and/or reproducing information signals, such as a magneto-optical disc or an optical disc. This disc is comprised of a disc-shaped base plate and a recording layer formed on at least one major surface of the base plate. The central portion of the disc is formed as a clamping portion which is retained by a disc driving unit of a recording and/or reproducing apparatus adapted for recording and/or reproducing information signals on or from the disc. The portion of the disc lying around the clamping portion is reserved as a signal recording area on or from which the information signals are written or read.
Referring to FIGS. 1 and 2, there has hitherto been proposed a disc cartridge comprised of a cartridge body 102 and a shutter member 104 which is accommodated within the cartridge body for preventing deposition of dust and dirt on a disc 101 or injuries thereto due to contact especially with hands or fingers as well as for facilitating handling of the disc 101. The disc 101 accommodated within the cartridge body 102 may be rotated therein by disc rotating means. Referring to FIG. 2, the major surface of the cartridge body 102 is formed with an aperture 103 by means of which at least a part of the signal recording surface of the disc may be exposed to outside ac ross its inner and outer peripheries. The information signals may be recorded and/or reproduced on or from the signal recording area by means of the disc recording and/or reproducing apparatus through the aperture 103.
The disc cartridge is provided with a shutter member 104 for closing the aperture 103 during non-use the disc cartridge as shown in FIG. 1 for protecting the disc 101 by preventing intrusion of dust and dirt into the inside of the cartridge body 102. The shutter member 104 is provided with a shutter portion 105 of a size large enough to close the aperture 103. The shutter portion 105 is formed with a through-hole 106 corresponding in size and shape to the aperture 103. The shutter member 104 is mounted for sliding along a lateral side of the cartridge body 102 by having its proximal end face 108 supported by a corresponding lateral side of the cartridge body 102. The shutter member 104 is supported for sliding between a first position of closing the aperture 103 by the shutter portion 105 as shown in FIG. 1 and a second position of opening the aperture 103 with the through-hole 106 in register with the aperture 103 as shown in FIG. 2.
Meanwhile, the shutter member 104 is constituted by bending a substantially rectangular metallic plate. The shutter member 104 may also be formed by bending a plate of synthetic resin or by integral molding of synthetic resin.
A recess 107 for guiding the shutter portion 105 is formed on the major surface of the cartridge body 102 in an area thereof corresponding to the travel passage of the shutter portion 105. The recess 107 is of a depth corresponding to the thickness of the shutter portion 105. Thus the upper surface of the shutter portion 105 is substantially flush with the major surface of the cartridge body 102 for the entire sliding stroke of the shutter member with respect to the cartridge body 102.
When loaded on the disc recording and/or reproducing apparatus, the disc cartridge is introduced at an entrance opening provided in the disc recording and/or reproducing apparatus with a direction normal to the sliding direction of the shutter member 104 as the inserting direction by an arrow d in FIG. 1.
At this time, the shutter member 104 is slid by a shutter member opening device, not shown, provided in the recording and/or reproducing apparatus, in a direction of opening the aperture 103, as shown by an arrow c in FIG. 2.
With the above described disc cartridge, if the disc cartridge is inserted at the entrance opening in a mistaken direction, there arises a risk that those portions of the cartridge body 102 not provided with the aperture 103 be abutted by a magnetic device or an optical head device provided in the disc recording and/or reproducing apparatus, possibly causing injuries or destruction of the magnetic device, optical head device or the cartridge body 102.
With a conventional disc cartridge, the length of a side of the cartridge body 102 parallel to its inserting direction shown by arrow a in FIG. 1, that is the side corresponding to a lateral side of the cartridge body 102, is selected to be longer than that of a side thereof normal to the inserting direction shown by arrow b in FIG. 1, that is a side corresponding to the forward side of the cartridge body 102. In such case, the mistaken operation of introducing the cartridge body 102 into the entrance opening in a direction normal to the proper inserting direction may be prevented by selecting the length of the entrance opening to be approximately equal to the length of the side of the cartridge body 102 normal to the proper inserting direction.
However, with such disc cartridge, since it is necessary to select the lengths of the lateral sides of the cartridge body 102 as described above, it becomes necessary to increase the size of the cartridge body beyond the minimum size required for accommodating the disc 101.
On the other hand, even if the length of the lateral side of the cartridge body 102 is selected to differ from that of its forward side, it is impossible to prevent mistaken inserting operations of inserting the disc cartridge at the entrance opening with the rear side of the cartridge body as the leading end or of inserting the disc cartridge body in a topsy-turvied position.
It may be envisaged to provide first and second mistaken insertion inhibiting grooves 111, 113 on the lateral sides of the cartridge body 102, as shown in FIGS. 3 and 4, thereby preventing the disc cartridge from being introduced in the direction normal to the proper inserting direction without the necessity of enlarging the length of the lateral side of the cartridge body 102 shown by arrow a in FIG. 4. The first mistaken insertion inhibiting groove 111 is formed on the bottom surface of the cartridge body 102 for extending from the forward side towards the rear side of the cartridge body 102 when looking in its inserting direction shown by arrow d in FIG. 4. The second mistaken insertion inhibiting groove 113 is formed on the lateral side of the cartridge body 102 for extending from the leading side towards the trailing side of the cartridge body 102 when looking in its inserting direction shown by arrow d in FIG. 4. The distance between the grooves 111 and 113, indicated by double-headed arrow b in FIG. 4, is selected to be shorter than the length of the lateral side of the cartridge body 102 shown by double-headed arrow A in FIG. 4. In this manner, if lugs or the like mating with these grooves 111, 113 are provided in the vicinity of the entrance opening provided in the disc recording and/or reproducing apparatus, the cartridge body 102 may be positively prevented from being introduced into the entrance opening in the direction normal to its proper inserting direction.
However, there are occasions wherein indicating holes or grooves are formed on the outer lateral side of the cartridge body 102 for indicating disc types, such as a disc in which information signals may be recorded and reproduced, e.g. a magneto-optical disc, a disc in which information signals may be recorded and reproduced but in which information signals, once recorded, can not be erased, or a disc in which information signals can only be reproduced, e.g. an optical disc. With the above described disc recording and/or reproducing apparatus, it is necessary to adjust or switch the intensities of the magnetic field produced by the magnetic head as an external magnetic field generating device, operating or non-operating states or the light output of the optical pickup device, depending on the disc types. For this reason, microswitches or the like are provided in the disc recording and/or reproducing apparatus for detecting the presence or absence of these indicating holes or grooves for performing the adjusting or switching operations.
If the mistaken insertion preventing grooves are provided in the cartridge body already provided with these indicating holes or grooves, there arises a risk that the cartridge body becomes inferior in mechanical strength such that the disc 101 can not be protected positively. On the other hand, if the mistaken insertion inhibiting grooves are provided in the cartridge body, the area on the lateral side thereof to be reserved for the indicating holes or grooves becomes narrow so that the disc cartridge needs to be enlarged in size for providing these indicating holes or grooves.